Question: At full price, Melvin would pay $1.679$ dollars per liter of gasoline. Using his loyalty card, Melvin only pays $1.439$ dollars per liter. How much less does Melvin pay per liter using his loyalty card?
Answer: Full price $-$ price with card $=$ difference in price. $\begin{matrix} &&&&\\ &{1}.&6&7&9\\ -&{1}.&4&3&9\\ \hline &{0}.&2&4&0\\ \end{matrix}$ ${1}-{1}={0}$ Melvin pays $0.24$ dollars less per liter with his loyalty card.